When utilizing air springs in passenger cars, a largest possible air volume is to be used to obtain optimal suspension comfort. Mostly, there is insufficient space at the wheel because of chassis components such as a longitudinal control arm, brake and drive shaft. For this reason, this large air volume is subdivided into an air spring volume and an ancillary volume (see FIG. 1a). The ancillary volume can then be accommodated at a location in the vicinity such as in the engine compartment, in the longitudinal support, in the trunk, et cetera. Both volumes are then connected by a line having a cross section which is of such a dimension that an air exchange can take place very rapidly and without significant pressure loss. If the vehicle travels on cobblestones, for example, then the air spring contracts and expands in correspondence to the road speed at a high frequency. Each spring contraction operation and each spring expansion operation is associated with an air exchange which may not be hindered because the suspension comfort would otherwise be reduced.
A high suspension comfort means a reduced spring stiffness. In accordance with the above, this is achieved with a large air spring volume. It is, however, a disadvantage that the steering becomes loose. Likewise, for a low spring stiffness, the driving performance changes when braking, when accelerating, and in travel through a curve as well as with rapid avoidance maneuvers. This change in driving performance is in the direction of instability which is unwanted because driving safety is thereby affected.
In order to resolve this conflict between comfortable air spring design and stability of the driving performance, the above-described line is provided with a valve, which can be blocked (see FIG. 1b). During normal driving conditions, the valve is open and is open in such a manner that the valve presents no significant hindrance for the air exchange between the air spring and the ancillary volume. If the vehicle is now braked, accelerated or driven in a curve or is compelled to execute a rapid defensive maneuver, then the valve is abruptly closed by a control apparatus which can detect the driving state by means of sensors. Thus, the air spring and the ancillary volumes are separated from each other with the consequence that only the air spring volume is available for the suspension operation. The spring stiffness is therefore higher and the vehicle has a more stable driving performance.
The valve is again opened as soon as the control apparatus detects that none of the above-described driving conditions is present any longer. This opening operation has to be carried out in such a manner that a pressure difference between the air spring volume and the ancillary volume, which has possibly formed in the meantime, can be slowly compensated so that there is therefore no sudden drop or upward bucking of the vehicle. only when the pressure compensation is complete can the valve again be completely opened.
Valves for this purpose are known. They are mostly realized as precontrol valves in truck design wherein a small electromagnetic valve switches a large pneumatically actuated valve (see FIG. 2). The alternative is an electromagnetic actuation of the valve. In the design of passenger cars, there is, however, no corresponding compressed air source of sufficient power present in order to switch the pneumatically actuated valve. For this reason, only the electromagnetic actuation remains (see FIG. 3a).
Independently of the nature of the actuation (magnetic valve or pneumatically actuated valve), a large valve stroke is needed as a consequence of the large line cross section in order to clear or enable the cross section completely (FIG. 3b). If the cross-sectional area of the line is defined as AL=DL2xc2x7n/4, then the open cross section is characterized by AVR=LURxc2x7HR=DRxc2x7Hxc2x7HR for a circular valve seat. This results from the peripheral length LUR and the stroke HR. In order that there be no constriction, both cross-sectional areas AL and AVR have to be of the same size so that: HR=DR/4. In practice, this means a stroke HR of approximately 5 mm for DL=20 mm.
Two disadvantages are associated with the large stroke. First, the actuating force of an electromagnet drops disproportionately with distance becoming ever greater. Accordingly, for valve actuation, an electromagnet is required which has a larger number of turns having low resistance and therefore also having a large valve mass and introducing a high cost. Secondly, armature and sealing body of the valve are accelerated by its spring in the direction toward the valve seat when switching off the actuating current. As a consequence of the large stroke, high speeds and large decelerations become effective when landing on the valve seat; that is, the sealing body generates a noise when striking the valve seat, which can be similar to the blow of a hammer.
In truck air spring systems, valves exist for rapid closing and slow opening on the basis of a pneumatic actuation.
Magnetic valves are known in passenger car air springs and have been adapted to the larger line cross section. Additionally, a pressure relief has been provided in order to reduce the acting forces. However, all of these solutions are associated with friction and do not permit a trouble-free adjustment or control. In the manufacture of trucks, the valves are pneumatically actuated because the pneumatic has a higher energy density. The high energy consumption (compressed air escapes) is of no essential significance. Likewise, the switching noise is also of no great consequence.
It is an object of the invention to provide a valve for a motor vehicle air spring.
The valve of the invention is for a motor vehicle air spring system including an air spring volume and an ancillary volume. The valve is mounted between the air spring volume and the ancillary volume and the valve includes: an inlet having a cross section (AL) and an outlet having a cross section (AL); a star nozzle defining a valve seat and being disposed between the inlet and the outlet; a valve body movable between a first position wherein the valve body is in contact engagement with the valve seat to close a flow path between the air spring volume and the ancillary volume and a second position wherein the flow path is at least partially open; the star nozzle including a nozzle body having a plurality of mutually intersecting slots (ns) formed concentrically therein; each of the slots having a length (Ds) and a width (SS); the star nozzle having a peripheral length (LUS) increased with respect to the peripheral length (LUR) of a round nozzle with the valve having a valve cross section (AVS) given by AVS=LUS*HS wherein HS is star nozzle stroke and the star nozzle stroke is given by Hs=AVS/LUS wherein the peripheral length (LUS) is given by LUS=Ds*Ss*ns; the star nozzle having a pass-through cross section (ADS) corresponding to the valve cross section (AVS) and being so large that the pass-through cross section (ADS) corresponds at least to the cross section (AL) Of the inlet and the outlet; and, the nozzle body having a valley-like recess formed between each two mutually adjacent ones of the slots.
The valve of the invention has the following characteristics, namely:
a) small mass;
b) low consumption of electrical energy;
c) full cross section without throttling;
d) very short reaction time;
e) stable performance in the presence of flow forces;
f) tight blocking of the line;
g) finely metered continuous opening;
h) no disturbing noise; and,
i) cost effective.
According to the invention, a star nozzle is used in lieu of a circular valve seat. This star nozzle (FIG. 5) is characterized in that a desired number of slots nS having the length DS and the width sS are concentrically arranged and mutually intersect. As a special case, a nozzle with nS=1 is considered wherein the slot is long and narrow. The star nozzle peripheral length LUS is increased relative to that of the round nozzle LUR and thereby the following applies for the valve cross section AVS=LUSxc2x7HS. The required stroke HS is significantly less than the stroke HR of the circular nozzle for a corresponding configuration (nS, DS, sS, RS). The throughput cross section ADS of the star nozzle must be so large that it corresponds at least to the cross section AL of the line. On the outside of the nozzle, there is a valley-like recess between each two mutually adjacent ones of the slots with this valley-like recess having a triangular cross-sectional surface. These function to make possible the access of the inflowing air to the inner part of the star. As a consequence of the star nozzle, the valve stroke can be significantly less. For this reason, fewer turns of an electromagnet (for the same current) are sufficient. The valve is more cost effective, smaller and lighter because of the fewer turns. Or, as a consequence of the smaller stroke, the current can be reduced so that less energy is consumed. The sealing body and armature are braked to a lesser extent with the impact against the valve seat because of the smaller stroke whereby less noise is produced. The electromagnet can be operated along the steepest portion of its characteristic line as a consequence of the small stroke. The valve is therefore insensitive to flow forces and has a stable characteristic line.
The sealing body is secured against rotation by the form of the collar (FIG. 4). Every indentation in the seal body always comes to the same location of the star nozzle as a consequence of the hold against rotation. Accordingly, permanent deformations (rubber pressure residual deforming) have no negative effects. Because the collar is made of rubber, the movement is dampened via the material damping and this reduces noise.
The star nozzle can be positioned at an angle (FIG. 6). In this way, a gearing in effect develops and the opening operation can be metered with a greater precision. The star nozzle can be provided with a second membrane (FIG. 7) or, preferably, with two rolling membranes as disclosed in parallel patent application Ser. No. 09/863,269, filed on May 24, 2001, and corresponding to German patent application 100 25 753.4, filed May 24, 2000, and incorporated herein by reference. The pressure is likewise applied to this second membrane and this leads to a relief of pressure. Because of the pressure differences reduced thereby, the forces are smaller and this leads to an additional reduction of the size needed. Compared to conventional pressure reliefs, this type of pressure relief affords the advantage that no tolerance problems and no frictional forces occur.
The star nozzle can basically be connected to any drive. Advantageous drives are: a step motor as a linear motor, a piezo stack actuator (also with path conversion), piezo bending element actuator (torque block), electrochemical actuator, pneumatic actuator (precontrol valve). A very precise positioning and energy cutoff after reaching the desired position is possible with a step motor. With a piezo actuator, there is a very low consumption of energy and a very high accuracy as to position as well as a very short reaction time. with an electrochemical actuator, the following are obtained: very low consumption of energy, very high holding forces, high position accuracy even after switchoff of the energy supply and a defined fail-safe condition. With a pneumatic actuator, very short actuating times and very small control valves are obtained.
Overall, the star nozzle valve of the invention has the following advantageous characteristics, namely: small structural space required; low mass; short switching times; low noise development; low manufacturing costs; low power consumption; and, good operating stability.
The star nozzle valve according to the invention is suitable in all areas where a large cross section must be cleared with small switching times and forces.